Peak to peak detect method to protect seek/settle induced encroachment

ABSTRACT

A system and method for improving write integrity of a magnetic storage system. A settling algorithm counter is reset if a position error signal of the write head indicates the head is vibrating with mechanical oscillations outside a predetermined threshold.

FIELD OF THE INVENTION

The present invention relates generally to magnetic storage technology.More particularly, the present invention relates to protecting dataintegrity from mechanical resonance in a magnetic storage system.

BACKGROUND OF THE INVENTION

Technological advances in magnetic storage allow data to be stored inever smaller physical dimension. For example, track widths in magnetictape or disk storage have become so small that mechanical vibrationswhich once were irrelevant can now cause writing errors. For examplewhen a read/write head positions itself over a desired track,oscillations on the mechanical structure of the head can be large enoughthat a write function writes data outside the allowed track width,resulting in write error.

When a read/write head operates, it is moved in a seek operation. Thisoperation locates and moves the head to the proper position for, e.g.,writing data. When the seek operation ends and the head is in position,there is a time period during which vibrations in the head must beallowed to settle. To deal with problems of this nature, settlingalgorithms are typically used which monitor the transient response andattempt to prevent write operations until the settling is completed.Shorter settling times typically permit more errors, while longersettling times, though less error prone, increase access and/or writetime for the apparatus. Hence, settling times are typically kept asshort as possible while still preventing as many errors as possible.

Non-consecutive settling algorithms employ multiple samples to determinewhether settling has occurred. For example, if 2 consecutive positionerror signal (PES) samples are within 8% of track pitch and thecorresponding velocity is within 6% of track pitch, then a settlingcounter of the algorithm is decreased by one. If this happens apredetermined number of times (e.g., 8 times in some implementations)the settling count reaches zero and settling is considered complete.

While such algorithms greatly decrease write error rate, certainfrequency mechanical oscillations can still cause the settling algorithmto fail. For example, seek-induced coil bending resonance createsmechanical oscillations in the range of 900-1600 Hz, which can causewrite errors despite the settling algorithm. The consequences of failurelead directly to reliability failure due to data encroachment outsidethe desired track, caused by data written with marginal PES.

Hence, the present state of the art would benefit from improvements towrite operations that further limit these errors without unnecessarilyextending the delay in write operations.

The present invention provides a solution to this and other problems.

SUMMARY OF THE INVENTION

The present invention involves a system and method for improvingalignment of heads in magnetic storage systems. In a preferredembodiment, an algorithm is implemented that detects movement by thehead outside a threshold, indicating the head is not yet settled. In apreferred embodiment, this information is obtained from the PES. Upondetecting such movement outside the threshold, the settling counter isreset so that the settling algorithm continues to run. Thus, the presentinvention provides a way to determine if settling is complete, andresets it if it is not.

This innovation provides a check on the settling algorithm, and thusprevents data writing if the drive is oscillating. It also allows normaloperation of the settling algorithm if there is no oscillation, and ishence invisible when it is not needed.

In one example embodiment, the present invention detects the peak topeak movement of the write head by monitoring a PES signal. If movement(for example) is beyond a threshold distance from track center, thesettling counter is reset. Noise and other irrelevant signals such ashigh frequency vibrations that will not affect alignment are preferablyfiltered by incorporating a low pass filter on the peak to peakdetector.

The present invention also can be implemented as a computer-readableprogram storage device which tangibly embodies a program of instructionsexecutable by a computer system to implement the innovative system andmethod.

These and various other features as well as advantages whichcharacterize the present invention will be apparent upon reading of thefollowing detailed description and review of the associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a magnetic disk drive consistent with a preferredembodiment.

FIG. 2 is a block diagram of the printed circuit board of the magneticdisk drive system.

FIG. 3 shows an oscilloscope capture of a PES output demonstratingsettling of a write head.

FIG. 4 shows an oscilloscope capture of a PES output implementing apreferred embodiment of the present invention.

FIG. 5 shows an oscilloscope capture of a PES output implementing apreferred embodiment of the present invention.

FIG. 6 shows a flow chart for process steps implementing a preferredembodiment of the present invention.

FIGS. 7-1 and 7-2 show flow charts for implementing a preferredembodiment of the present invention.

DETAILED DESCRIPTION

Referring now to the drawings, and initially to FIG. 1, there isillustrated an example of a disc drive designated generally by thereference numeral 20. The disc drive 20 includes a stack of storagediscs 22 a-d and a stack of read/write heads 24 a-h. Each of the storagediscs 22 a-d is provided with a plurality of data tracks to store userdata. As illustrated in FIG. 1, one head is provided for each surface ofeach of the discs 22 a-d such that data can be read from or written tothe data tracks of all of the storage discs. The heads are coupled to apre-amplifier 31. It should be understood that the disc drive 20 ismerely representative of a disc drive system utilizing the presentinvention and that the present invention can be implemented in a discdrive system including more or less storage discs.

The storage discs 22 a-d are mounted for rotation by a spindle motorarrangement 29, as is known in the art. Moreover, the read/write heads24 a-h are supported by respective actuator arms 28 a-h for controlledpositioning over preselected radii of the storage discs 22 a-d to enablethe reading and writing of data from and to the data tracks. To thatend, the actuator arms 28 a-h are rotatably mounted on a pin 30 by avoice coil motor 32 operable to controllably rotate the actuator arms 28a-h radially across the disc surfaces.

Each of the read/write heads 24 a-h is mounted to a respective actuatorarm 28 a-h by a flexure element (not shown) and comprises a magnetictransducer 25 mounted to a slider 26 having an air bearing surface (notshown), all in a known manner. As typically used in disc drive systems,the sliders 26 cause the magnetic transducers 25 of the read/write heads24 a-h to “fly” above the surfaces of the respective storage discs 22a-d for non-contact operation of the disc drive system, as discussedabove. When not in use, the voice coil motor 32 rotates the actuatorarms 28 a-h during a contact stop operation, to position the read/writeheads 24 a-h over a respective landing zone 58 or 60, where theread/write heads 24 a-h come to rest on the storage disc surfaces. Asshould be understood, each of the read/write heads 24 a-h is at rest ona respective landing zone 58 or 60 at the commencement of a contactstart operation.

A printed circuit board (PCB) 34 is provided to mount controlelectronics for controlled operation of the spindle motor 29 and thevoice coil motor 32. The PCB 34 also includes read/write channelcircuitry coupled to the read/write heads 24 a-h via the pre-amplifier31, to control the transfer of data to and from the data tracks of thestorage discs 22 a-d. The manner for coupling the PCB 34 to the variouscomponents of the disc drive is well known in the art, and includes aconnector 33 to couple the read/write channel circuitry to thepre-amplifier 31.

Referring now to FIG. 2, there is illustrated in schematic form of thePCB 34 and the electrical couplings between the control electronics onthe PCB 34 and the components of the disc drive system described above.A microprocessor 35 is coupled to each of a read/write control 36,spindle motor control 38, actuator control 40, ROM 42 and RAM 43. Inmodern disc drive designs, the microprocessor can comprise a digitalsignal processor (DSP). The microprocessor 35 sends data to and receivesdata from the storage discs 22 a-d via the read/write control 36 and theread/write heads 24 a-h.

The microprocessor 35 also operates according to instructions stored inthe ROM 42 to generate and transmit control signals to each of thespindle motor control 38 and the actuator control 40. The spindle motorcontrol 38 is responsive to the control signals received from themicroprocessor 35 to generate and transmit a drive voltage to thespindle motor 29 to cause the storage discs 22 a-d to rotate at anappropriate rotational velocity.

Similarly, the actuator control 40 is responsive to the control signalsreceived from the microprocessor 35 to generate and transmit a voltageto the voice coil motor 32 to controllably rotate the read/write heads24 a-h, via the actuator arms 28 a-h, to preselected radial positionsover the storage discs 22 a-d. The magnitude and polarity of the voltagegenerated by the actuator control 40, as a function of themicroprocessor control signals, determines the radial direction andradial speed of the read/write heads 24 a-h.

When data to be written or read from one of the storage discs 22 a-d arestored on a data track different from the current radial position of theread/write heads 24 a-h, the microprocessor 35 determines the currentradial position of the read/write heads 24 a-h and the radial positionof the data track where the read/write heads 24 a-h are to be relocated.The microprocessor 35 then implements a seek operation wherein thecontrol signals generated by the microprocessor 35 for the actuatorcontrol 40 cause the voice coil motor 32 to move the read/write heads 24a-h from the current data track to a destination data track at thedesired radial position.

When the actuator has moved the read/write heads 24 a-h to thedestination data track, a multiplexer (not shown) is used to couple thehead 24 a-h over the specific data track to be written or read, to theread/write control 36, as is generally known in the art. The read/writecontrol 36 includes a read channel that, in accordance with modern discdrive design, comprises an electronic circuit that detects informationrepresented by magnetic transitions recorded on the disc surface withinthe radial extent of the selected data track. As described above, eachdata track is divided into a number of data sectors.

During a read operation, electrical signals transduced by the head fromthe magnetic transitions of the data sectors are input to the readchannel of the read/write control 36 for processing via thepre-amplifier 31. The RAM 43 can be used to buffer data read from or tobe written to the data sectors of the storage discs 22 a-d via theread/write control 36. The buffered data can be transferred to or from ahost computer utilizing the disc drive for data storage. Positiondetector 44 also accepts output from the head 24 that charts the headmovement in both position and time to ultimately create a position errorsignal (PES).

The present invention incorporates a method of detecting peak to peakdistance of a PES signal during settling mode. The PES signal ismonitored to detect two consecutive PES peak values (a positive and anegative peak) and if the peaks are outside a predetermined threshold,then the settling count is reset or the settling criteria arereinitialized.

A further implementation includes checking the time distance between thetwo consecutive peaks. If the two peaks are within a predetermined timeof one another (indicating the oscillations are above a predeterminedfrequency) then the response is ignored. This feature helps ensure thathigh frequency noise that will not affect head alignment do not triggerresetting of the settling algorithm. This feature can also beimplemented as a low pass filter in some embodiments, as detailedfurther below.

FIG. 3 shows an oscilloscope capture of a PES output. The horizontalaxis unit is time, the vertical axis unit is distance perpendicular tothe track. In this example, a single drive head trace is shown. Trace D302 is the PES output, trace B 304 is the settling window. When trace Bis high, the head is moving through tracking mode or otherwise is notsettled. When trace B is at a low level, the servo is either in seekmode or in track follow mode, and the head is considered settled by thesystem, meaning write is allowed. In track follow mode, read/writefirmware allows writing data to the disc. In FIG. 3, the data begins (onthe left of the graph) with the PES going through high frequencyoscillations. These oscillations decrease in frequency, at which timethe system enters settling mode (where trace B goes high). The servoswitches from tracking mode back to settle mode several times before itfinally stays within tracking mode. Note the multiple short durationtransitions from high to low of the B trace. These oscillations willcause data to be written with marginal PES, or even PES slightly abovethreshold because of the time delay before the servo is made aware thatthe PES is outside the settling threshold. Hence, in this example, datais written during time periods when the settling algorithm is unaware oflarge PES values.

FIG. 4 shows a scope capture showing the results of the presentinnovation. Again, trace D 402 is the PES, which oscillates with similarfrequency as in FIG. 1 when it enter settling mode. Trace B 404, thesettling window, stays in settling mode until the PES oscillationamplitude falls within a threshold track pitch peak to peak value. Inthis example, a threshold of 24% track pitch is used. The pulses oftrace C 406 indicate where the peak to peak detection algorithm isfunctioning, resetting the settling count. On the left half of thegraph, where the PES 402 is not settled within threshold levels, trace B404 shows a high (unsettled) state. But note that trace C indicates thesettling count is reset a number of times during trace B's high period.The resetting of the count is indicated in trace C by the spikes, whichare aligned with the PES signal where it goes beyond the threshold.

In a preferred embodiment, the present invention is invisible to thesystem in cases where it is not needed. In other words, the peak to peakdetection function should not delay writing in situations where it isnot invoked. FIG. 5 shows a scope capture demonstrating this propertyfor the presently preferred embodiment. This figure shows a sequentialseek/settling scope capture where the coil bending mode was not excited,shown by trace D 502. The smooth PES transient from settle to trackfollow mode is shown by trace B 504, which has one section in a highstate (depicting unsettled tracking mode). Since there are no transientpeak movements outside the threshold, trace C 506, which representsdetection of peak to peak distance beyond the threshold, shows nomovement. Hence, the present invention does not affect normal operationof the write head unless settling failure is indicated.

FIG. 6 shows a flow chart for a process implementing a preferredembodiment of the present invention. In a preferred embodiment, thepresent invention is implemented in the servo actuator control 40. Itshould be noted that other implementations are possible. The preferredexample process starts with initialization of the settling algorithmparameters, including the settling algorithm count (step 602). Next, thethreshold value for allowed offset of the read/write head is set,preferably by setting a minimum and maximum value for the peakthresholds (step 604). The first peak is detected (step 606) then thefollowing peak is detected (step 608). A determination is made whetherthe time difference between the two peaks is greater than apredetermined time threshold (step 610). If the time difference betweenthe occurrence of the two peaks is below a predetermined time threshold,then the process returns (step 612). This step allows filtering of highfrequency noise from the response, and helps prevent invocation of thesettle counter reset when unnecessary. If the time difference is abovethe predetermined time threshold, indicating a relatively low frequency(˜900-1600 Hz) mechanical resonance oscillation, then the process checksthe distance between the two peaks to determine if the peak to peakmaximum is beyond the allowed threshold (step 614). If the peak to peakdistance is within the threshold, the process returns (step 616) andcontinues monitoring peak to peak distance. If the peak to peak distanceis outside the threshold, the settling counter of the settling algorithmis reset (step 618). The process then returns to monitoring peak to peakdistance (step 620).

The present invention guarantees that data is written with a small PESby tuning the peak to peak value limit. In an alternative embodiment, alow pass filter is added. Such a filter makes the detection algorithmmore robust to high frequency noise, and prevents resetting of thesettling algorithm due to such noise. A low pass filter can also be usedin lieu of or in addition to the minimum time between peaks thresholddiscussed in FIG. 6. Both implementations filter out high frequencynoise. Also in a preferred embodiment, the first peak detected by thedetection algorithm is ignored because it is typically caused by normaltracking overshoot/undershoot. Eliminating the first peak detected fromconsideration prevents resetting of the settling algorithm counter whentracking overshoot/undershoot occurs but when no mechanical vibrationsare present. This reduces the number of times the settling counter isreset in situations where resetting is not necessary.

It should be noted that although the preferred embodiment shows the timethreshold between peaks is determined in the process before the physicaldistance between the peaks is determined, the order of these twodeterminations can be varied, detecting peak to peak distance before thetime, for example.

FIGS. 7-1 and 7-2 show a preferred implementation of the presentinvention. This example shows a protective peak to peak detect algorithmthat works on top of existing settling criteria, without generatingdrive performance loss for cases where the protective algorithm is notinvoked. The algorithm is preferably robust to high frequency noisewhich might be caused by electrical noise or servo channel demodulationerrors. Preferably there is no logical code change for any existingnon-consecutive settling criteria. The protective algorithm ispreferably designed to capture multiple frequencies, for example, in the900 Hz to the 1600 Hz range. It preferably also does not generate falsetriggers caused by normal seek arrival induced PES over or undershoot.

In the flow of FIGS. 7-1 and 7-2, the following terms are used.

-   PrimeTFSettle: it is code subroutine name, where some parameters    used to qualify a seek/settle process will be initialized.-   AvgVelocityML: header moving average velocity Bset/bclr: set/clear a    bit (assembly code)-   NextIsMin/Peak2PeakStart/ResetStart: bit variable defined in the    assembly code-   REGXToGoML: header moving position error variable-   PeakSettleXmin: variable defined in the code for negative peak-   PeakSettleXmax: variable defined in the code for positive peak-   TrkFollowSetl: code subroutine name where qualifies settling process-   PeakSettleTimeMin: variable defined to recode time when negative    peak happens-   PeakSettleTimeMax: variable defined to recode time when positive    peak happens-   PEAK_POS_THRESH: constant value defined in the code for peak to peak    threshold-   SRVO_SEC_RESET_CNT: constant value defined in the code for timing    threshold between peak to peak-   Reset Settle Counts: code label where the algorithm is trigged and    reset the settling qualification

FIG. 7-1 generally shows an algorithm for initialization of theinnovative process. The settling algorithm parameters are initializedand criteria for the peak to peak protective algorithm are also set.FIG. 7-2 shows an example algorithm for implementation of the innovativeprocess to determine whether the head is settled.

It is important to note that while the present invention has beendescribed in the context of a fully functioning data processing system,those of ordinary skill in the art will appreciate that the processes ofthe present invention are capable of being distributed in the form of acomputer readable medium of instructions or other functional descriptivematerial and in a variety of other forms and that the present inventionis equally applicable regardless of the particular type of signalbearing media actually used to carry out the distribution. Examples ofcomputer readable media include recordable-type media, such as a floppydisk, a hard disk drive, a RAM, CD-ROMs, DVD-ROMs, and transmission-typemedia, such as digital and analog communications links, wired orwireless communications links using transmission forms, such as, forexample, radio frequency and light wave transmissions. The computerreadable media may take the form of coded formats that are decoded foractual use in a particular data processing system. Functionaldescriptive material is information that imparts functionality to amachine. Functional descriptive material includes, but is not limitedto, computer programs, instructions, rules, facts, definitions ofcomputable functions, objects, and data structures.

The description of the present invention has been presented for purposesof illustration and description, and is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the art. Theembodiment was chosen and described in order to best explain theprinciples of the invention, the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

1. A method comprising steps of: detecting a first peak of a positionerror signal of a write head; detecting a second peak of the positionerror signal of the write head, the second peak following the first peakand being of opposite sign with respect to the first peak; and comparinga distance between the first and second peaks with a distance threshold.2. The method of claim 1, further comprising: comparing a time durationbetween the first and second peaks with a time threshold.
 3. The methodof claim 2, further comprising: if the duration between the first andsecond peaks is greater than the time threshold and if the distancebetween the first and second peaks is greater than the distancethreshold, resetting a settling algorithm.
 4. The method of claim 1,further comprising: if the distance between the first and second peaksis greater than the distance threshold, resetting a settling algorithm.5. The method of claim 4, wherein the step of resetting the settlingalgorithm comprises resetting a counter of the settling algorithm. 6.The method of claim 1, wherein a low pass filter filters out highfrequency oscillations from the position error signal.
 7. A method forcontrolling operations of a storage device, the method comprising stepsof: detecting a position error signal of a head of the storage device,the position error signal having at least two consecutive peaks ofopposite sign; comparing a distance between the two consecutive peaks toa distance threshold; delaying a write operation if the distance betweenthe two consecutive peaks is greater than the distance threshold.
 8. Themethod of claim 7, wherein the write operation is only delayed if aduration between the two consecutive peaks is greater than a timethreshold.
 9. The method of claim 7, wherein the write operation isdelayed by resetting a settling counter of a settling algorithm.
 10. Themethod of claim 7, further comprising a filter which filters highfrequency oscillations out of the position error signal.
 11. A storagesystem, comprising: a storage medium having locations; a head capable ofwriting to the storage medium; and a position detection system forproducing a position error signal of the head relative to the locationsof the storage medium; wherein if the position error signal includes twopeaks outside a position error threshold, a write operation is halted.12. The system of claim 11, wherein the two peaks are consecutiveopposite sign peaks.
 13. The system of claim 11, wherein the writeoperation is halted by resetting a counter of a settling algorithm. 14.The system of claim 11, further comprising a low pass filter thatfilters out high frequencies of the position error signal.
 15. Thesystem of claim 11, wherein the write operation is only halted if thetwo peaks are consecutive peaks of opposite sign and if the two peaksoccur with at least a predetermined amount of time between them.
 16. Amethod of comprising the steps of: detecting a position error signal ofa head in a magnetic storage system relative to tracks of the magneticstorage system; resetting a settling algorithm if the position errorsignal detects mechanical oscillations of the head outside apredetermined position error signal threshold.
 17. The method of claim16, wherein the step of resetting the settling algorithm comprisesresetting a counter of the settling algorithm.
 18. The method of claim16, wherein the settling algorithm is reset only if the head movesoutside the predetermined position error signal threshold with afrequency above a predetermined frequency.
 19. The method of claim 16,further comprising a low pass filter that filters frequencies above 1600Hz from the position error signal.